1. Field of the Invention.
The present invention relates generally to processing poultry for human consumption, and, in particular, to a method and apparatus for automatically electrically stimulating poultry carcasses in poultry plants to tenderize the poultry meat.
2. Discussion of Related Art.
The consumer demand for poultry in recent years has shifted from fresh, whole carcasses to fresh, cut-up poultry and other processed poultry products. Due to the muscle tensioning associated with rigor mortis, poultry carcasses need to be aged for four to six hours to obtain poultry breast meat which is sufficiently tender for human tastes. Because deboning non-aged poultry carcasses produces meat that is unacceptably tough to the consumer, because storing poultry carcasses for a lengthy aging period to obtain tender poultry meat is expensive, and because storing increases the risk of microbial growth and decomposition of the meat, numerous studies have been conducted in an effort to find a way to accelerate the aging process.
One line of investigation has been directed toward the electrical stimulation of poultry carcasses promptly after their slaughter as a result of some degree of acceptance of electrical stimulation of beef carcasses in the meat-packaging industry to accelerate the aging process. Wide disagreement, however, continues to exist within the beef industry over the best specific type of electrical stimulation.
Broadly speaking, three general types of electrical stimulation have received some acceptance in the meat-packing industry. In one approach, pulses in excess of 1000 volts are applied to a carcass rubbing against an electrified rail. In a second approach, high voltage pulses are applied across the hind legs of the beef carcass. In both of these approaches, electrical stimulation occurs for a period in excess of 90 seconds and in some instances for several minutes. In a third approach, a series of low voltage pulses on the order of 20 volts are applied through a rectal probe for at least 90 seconds. In each of these methods, the periods of high current flow are minimized in comparison to the spacing between the pulses to minimize or avoid burning the meat. However, due to the differences in size and meat composition, and biochemical and physiological differences in the nerve and muscle systems of beef and poultry, such approaches provide little guidance for the poultry processing industry.
As discussed in "Electrical Stimulation in Poultry, A Review and Evaluation," by Yanblin Li, T. J. Siebenmorgen, and C. L. Griffis, 1993 Poultry Science, numerous laboratory studies of electrical stimulation of poultry meat have been conducted since 1960, with most of the activity involving chickens conducted since 1986. Although numerous different voltages, currents, and stimulation times have been used in such studies, most have been directed to the use of high voltage pulses above 440 volts separated by periods of no stimulation, as exemplified by "Fragmentation, Tenderness and Post-Mortem Metabolism of Early-Harvested Boiler Breast Fillets from Carcasses Treated with Electrical Stimulation and Muscle Tension," by S. G. Birkhold and A. R. Sams, 1993 Poultry Science, March 1993.
The studies to date relating to the electrical stimulation of poultry have been inconclusive because the optimum electrical parameters, the electrical properties of poultry meat, and the biochemical and physiological responses of poultry nerve and muscle systems to electrical stimulation have not been known. Further, there has yet to be developed a practical method of automatically electrically stimulating poultry meat in poultry processing plants in order to effectively tenderize poultry breast meat without additional aging of the poultry carcasses in storage areas at the plant site.
Additionally, it has been found that skin weakness of the poultry causes skin tears which are undesirable but sometimes unavoidable in the electrical stimulation process. A need exists to minimize skin tears, or to have the skin tears occur in parts of the poultry carcass not to be utilized for human consumption, or in the less expensive portions of the carcass.